The role of [His7]-corazonin in the control of body-color polymorphism in the migratory locust, Locusta migratoria (Orthoptera: Acrididae)

The effect of [His7]-corazonin on the body color in Locusta migratoria was examined by varying the injected dose and the time of injection in both an albino and a normal (pigmented) strain. Albino nymphs injected with a high dose (100 pmol) of [His7]-corazonin at the beginning of the third instar turned completely black in the following instar, whereas those injected with the same dose in the middle of the instar developed black patterns with an orange background color, the body coloration characteristic of normal gregarious (crowded) individuals. Injection at the end of the third instar induced a reddish color with few black spots. Irrespective of the time of injection of the peptide, most of these individuals became completely black after ecdysis to the fifth instar. A similar result was obtained with a lower dose (1 pmol), although the color expressed was lighter. In the normal strain, injection of 1 nmol or 100 pmol into crowded third instar nymphs also caused most of them to become completely black in the fourth and fifth instars, but a lower dose apparently had no influence. These results suggest that the temporal changes in hemolymph titer of [His7]-corazonin are important in the expression of body color in L. migratoria.